Phosphorylated dialdehydes will be prepared and condensed with purified human hemoglobin to form Schiff bases which will be reduced to form stable covalent bonds. The products will be fractionated by ion exchange chromatography and subjected to electrophoresis. Oxygen loading curves will be determined. Solutions of selected products will be transfused in rats and rabbits to determine the duration of retention in the circulation and the effects on the animals.